Moisture sensor

Abstract

A novel and useful sensor and sensing system employs a transmission electrode which provides a length of transmission electrode that is greater than the physical length of the sensor, allowing for the effective and accurate determination of the moisture content of a volume of material using high-frequency measurement methods. The construction of the sensor allows the sensor to be directly inserted into the material, without requiring excavation or backfilling of the sensors in the material. The sensor can be employed as part of a sensing system, with one or more sensors preferably being managed by a field node, which in turn, interoperates with a system master node.

1. A sensor for sensing the moisture content of a volume of material surrounding the sensor, the sensor comprising:
 an electrical circuit for implementing a high frequency method for measuring moisture content, the electrical circuit having a signal transmission electrode connected thereto; 
 a mounting substrate supporting the electrical circuit and the signal transmission electrode; 
 the signal transmission electrode having an electrical length greater than a physical length of the mounting substrate; and 
 a sensor body encapsulating the mounting substrate and the electrical circuit, at least the portion of the sensor body contacting the electrical circuit being non-conductive, wherein the mounting substrate is a printed circuit board, and wherein the signal transmission electrode is a composite electrode comprising a plurality of serially connected conductive segments located on both sides of the printed circuit board. 
 
     
     
       2. The sensor of  claim 1 , wherein the length of the signal transmission electrode is greater than twice the physical length of the mounting substrate. 
     
     
       3. The sensor of  claim 1 , wherein the length of the signal transmission electrode is greater than a physical perimeter of the mounting substrate. 
     
     
       4. The sensor of  claim 1 , wherein the plurality of serially connected conductive segments are located on alternating sides of the printed circuit board, each of the plurality of serially connected conductive segments being connected to the subsequent one of the plurality of serially connected conductive segments by a conductive via extending between opposing sides of the printed circuit board. 
     
     
       5. The sensor of  claim 1 , the sensor body comprising a rigid carrier frame and a non-conductive dielectric sheath about the mounting substrate and the electrical circuit. 
     
     
       6. The sensor of  claim 1 , the electrical circuit being configured to apply one or more electrical pulses to an input of the signal transmission electrode, and further being configured to analyze the response characteristics of the one or more electrical pulses received at an output of the signal transmission electrode. 
     
     
       7. The sensor of  claim 1 , the electrical circuit being configured to apply one or more sinusoidal electrical signals to an input of the signal transmission electrode, and further being configured to analyze at least one of the magnitude and phase characteristics of the one or more sinusoidal electrical signals received at an output of the signal transmission electrode. 
     
     
       8. The sensor of  claim 1 , wherein the sensor body comprises a first tapered end for facilitating insertion into the material to be sensed. 
     
     
       9. The sensor of  claim 1 , wherein the sensor body comprises a second end opposite the first end for receiving a force to drive the sensor body into the material to be sensed. 
     
     
       10. The sensor of  claim 1 , further comprising:
 a cap coupled to the sensor body; 
 electrical connections protruding from the cap for supplying electrical power to the sensor; 
 the cap being configured to permit the cable to protrude at an angle between zero and ninety degrees with respect to a length of the sensor.